Wheelhouse robotic roller hemming

ABSTRACT

A robotic roller hemming apparatus includes a mounting member having a face for operative connection of the mounting member to a multi-axis controllable robotic arm, and a bracket extending from the face. A tracking roller is mounted on the bracket. A slide plate is operatively connected to the bracket and slidable relative to the bracket. A hemming roller is operatively connected to the slide plate proximate the tracking roller for roller hemming nested metal panels therebetween the hemming and tracking rollers. A slide actuator connects the bracket and the slide plate for moving the hemming roller toward and away from the tracking roller.

TECHNICAL FIELD

This invention relates to hemming of a bent edge of one or more preformed metal panels to form a hemmed joint or closed panel, and more particularly to an apparatus, system, and method for robotic roller hemming.

BACKGROUND OF THE INVENTION

It is known in the art relating to hemming of metal panels that roller hemming apparatus can be used to hem the edges of the metal panels forming automotive parts such as door panels, hood panels, and decklid panels.

Conventionally, a hemming apparatus may be mounted to a multi-axis controllable robot and may include a hem roller carried by a support. The conventional hemming apparatus is adapted for hemming a bent edge portion of a workpiece, such as a door panel, positioned on a hemming die, by rotating the hem roller under pressure along the bent portion. The conventional roller type hemming apparatus can thus be used for continuous hemming along the contour of the edge of the workpiece. This process, however, requires moving the workpiece to the hemming die and positioning the workpiece in the die.

Further, it is known to use a portable hemming die apparatus to hem a vehicle wheelhouse area. Such a portable hemming apparatus includes a hemming die set and may be mounted to a robot arm. The robot arm may then move the hemming die set to a workpiece to hem the workpiece. The hemming die, however, may be heavy and bulky to move. Also, each hemming die is specific to the shape and design of a certain workpiece. Hence, the hemming die must be changed when a different workpiece is introduced into a system.

SUMMARY OF THE INVENTION

The present invention provides a robotic roller hemming apparatus, system, and method that utilizes a single roller head for pre-hemming and final hemming that can compensate for various material thicknesses. The apparatus, system, and method requires just one programmed robot path to perform both pre-hemming and final hemming, thereby allowing for pre-hemming and final hemming along one path without the need to remove the roller head from the workpiece. The present apparatus, system, and method further allows for the hemming of a plurality of differently shaped workpieces using a single tooling fixture, and allows for adjustment of the pressure on the roller head to conform with various hemming product requirements.

More particularly, the present invention provides a dual robot system and method in which one robot carries a lightweight anvil and a second robot carries a universal roller hemming head apparatus including a hemming roller for both pre-hemming and final hemming of a workpiece such as a vehicle wheelhouse.

In one embodiment, a robotic roller hemming apparatus in accordance with the invention includes a mounting member having a face for operative connection of the mounting member to a multi-axis controllable robotic arm, and a bracket extending from the face. A tracking roller is mounted on the bracket. A slide plate is operatively connected to the bracket and slidable relative to the bracket. A hemming roller is operatively connected to the slide plate proximate the tracking roller for roller hemming nested metal panels therebetween the hemming and tracking rollers. A slide actuator connects the bracket and the slide plate for moving the hemming roller toward and away from the tracking roller.

The robotic roller hemming apparatus may further include a linkage assembly operatively connected to the mounting member and the hemming roller for pivoting the hemming roller relative to the mounting member, and a pivot actuator for actuating the linkage assembly to pivot the hemming roller. The linkage assembly may include a pivot bar having first and second opposite ends, the pivot bar first end being pivotally connected to the slide plate and the pivot bar second end being operatively connected to the hemming roller; a link bar having first and second opposite ends, the link bar first end being pivotally attached to the pivot bar second end adjacent the hemming roller; and a bell crank arm having first and second opposite ends, the bell crank arm first end being pivotally connected to the link bar second end and the bell crank arm second end being pivotally connected to the pivot actuator. The bell crank arm is pivotally connected to the slide plate intermediate its first and second ends. A stop may be mounted to the slide plate. The stop limits the pivotal movement of the pivot bar.

The pivot actuator may be mounted on the slide plate. The slide actuator may be mounted on the mounting member bracket. The mounting member bracket may include a linear track, and the slide plate is operatively engaged with the linear track and slidable along the linear track. The linear track may include a pair of rails, and the slide plate may include a pair of bearing blocks engaged with the pair of rails.

A dual-robot, robotic roller hemming system in accordance with the invention includes a first multi-axis controllable robotic arm having an end effecter that carries a hemming anvil. The system also includes a second multi-axis controllable robotic arm having a roller hemming head at an end thereof. The roller hemming head includes a tracking roller and a multi-positional hemming roller capable of performing both pre-hemming and final hemming operations. The hemming roller is adjustable between pre-hemming and final hemming positions and cooperable with the tracking roller and anvil to pre-hem and final hem a workpiece. The hemming roller performs pre-hemming and subsequent final hemming of the workpiece sequentially along a single hemming path.

The hemming roller may be positionable about an edge of the workpiece on one side of the workpiece, and the anvil may be positionable adjacent the workpiece about a side opposite the hemming roller. The first robotic arm may include a location unit for positioning the anvil relative to a workpiece. The first robotic arm end effecter may include a robotic tool exchange unit for interchanging the anvil with at least one alternative anvil. The system may also include an anvil storage unit for holding the at least one alternative hemming anvil. The anvil may include an attachment device for temporary attachment of the anvil to the workpiece. The attachment device may include an arrangement of vacuum cups.

The hemming roller may include an indexing feature cooperable with an edge of the anvil that allows for indexing of the hemming roller between pre-hemming and final hemming positions. The roller hemming head may include a servo positioner for adjusting the hemming roller between various pre-hemming and final hemming angular positions relative to the anvil. Alternatively, the roller hemming head may include an actuator for adjusting the hemming roller between various pre-hemming and final hemming angular positions relative to the anvil.

The tracking roller may be engagable with the anvil to aide in guiding the roller hemming head along the anvil. The roller hemming head may include a slide unit for compressing the workpiece and the anvil between the hemming roller and the tracking roller. The slide unit may linearly move the hemming roller to adjust the distance between the hemming roller and the tracking roller.

A method for robotic roller hemming in accordance with the invention includes providing a first multi-axis controllable robotic arm having an end effecter that carries a hemming anvil having a hemming surface and a tracking surface. A second multi-axis controllable robotic arm having a roller hemming head at an end thereof is also provided. The roller hemming head includes a hemming roller adjustable between pre-hemming and final hemming positions and a tracking roller proximate the hemming roller. The first robotic arm is employed to position the anvil hemming surface adjacent a workpiece. The hemming roller is adjusted to the pre-hemming position. The second robotic arm is employed to position the roller hemming head relative to the workpiece and the anvil such that the tracking roller contacts the anvil tracking surface and the hemming roller engages the workpiece. The second robotic arm is employed to move the roller hemming head along the anvil such that the tracking roller follows the anvil tracking surface and the hemming roller pre-hems the workpiece. The hemming roller is adjusted to the final hemming position. The second robotic arm is employed to move the roller hemming head along the anvil such that the tracking roller follows the anvil tracking surface and the hemming roller final hems the workpiece.

After the first robotic arm positions the anvil hemming surface adjacent the workpiece, the anvil may be temporarily attached to the workpiece to stabilize the anvil relative to the workpiece.

A path followed by the hemming roller during pre-hemming may also be followed by the hemming roller during final hemming. In other words, the pre-hemming and final hemming paths may be essentially identical. During final hemming, the hemming roller may follow the hemming path in the same direction of travel as during pre-hemming. Alternatively, the hemming roller may follow the hemming path in a reverse direction relative to a direction of travel followed during pre-hemming.

The roller hemming head may include a slide unit for engaging and disengaging the tracking roller with the anvil tracking surface and the hemming roller with the workpiece. The slide unit may be actuated to engage the tracking roller with the anvil tracking surface and the hemming roller with the workpiece prior to pre-hemming. The slide unit may also be actuated to disengage the tracking roller with the anvil tracking surface and the hemming roller with the workpiece after final hemming.

After the hemming roller final hems the workpiece, the second robotic arm may be employed to move the roller hemming head away from the workpiece, and the first robotic arm may be employed to move the anvil away from the workpiece.

These and other features and advantages of the invention will be more fully understood from the following detailed description of the invention taken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a perspective view robotic roller hemming apparatus in accordance with the invention for pre-hemming and final hemming nested metal panels;

FIG. 2 is a side view of the robotic roller hemming apparatus of FIG. 1;

FIG. 3 is a schematic view of an alternative embodiment of a robotic roller hemming apparatus in accordance with the invention in a pre-hemming position relative to an anvil and a workpiece, and a final hemming position partially shown in phantom;

FIG. 4 is an environmental view of a robotic roller hemming system in accordance with the invention including a multi-axis controllable robotic arm having the robotic roller hemming apparatus at an end thereof;

FIG. 5 is a schematic view of another multi-axis controllable robotic arm having an end effecter that carries a hemming anvil; and

FIG. 6 is a side view of the robotic roller hemming apparatus in a final hemming position relative to an anvil and a workpiece, and a pre-hemming position shown in phantom.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings in detail, numeral 10 generally indicates a robotic roller hemming apparatus in accordance with the invention. Turning first to FIGS. 1 and 2, the robotic roller hemming apparatus 10 includes a mounting member 12 having a face 14 for operative connection of the mounting member 12 to a multi-axis controllable robotic arm, and a bracket 16 extending from the face 14. A rotatable tracking roller 18 is mounted on the bracket 16. A slide plate 20 is operatively connected to the bracket 16 and slidable relative to the bracket. A multi-positional, rotatable hemming roller 22 is operatively connected to the slide plate 20 proximate the tracking roller 18 for roller hemming nested metal panels therebetween the hemming and tracking rollers. The hemming roller 22 is cooperable with the tracking roller 18 to perform sequential hemming operations along a single hemming path. Due to its multi-position capability, the hemming roller 22 can also perform both pre-hemming and final hemming operations by adjusting the angular orientation of the hemming roller 22 relative to the tracking roller 18. A slide actuator 24 connects the bracket 16 and the slide plate 20 for moving the hemming roller 22 toward and away from the tracking roller 18. The slide actuator 24 may include a piston 25 operatively connected to a flange 21 of the slide plate 20. The slide actuator 24 may be pneumatically operated, hydraulically operated, or similar.

In a specific embodiment, the robotic roller hemming apparatus 10 may further include a linkage assembly 26 operatively connected to the mounting member 12 and the hemming roller 22 for pivoting the hemming roller relative to the mounting member. A pivot actuator 28 actuates the linkage assembly 26 to pivot the hemming roller 22, thereby adjusting the hemming roller 22 between various pre-hemming and final hemming angular positions relative to a workpiece. The pivot actuator 28 may be pneumatically operated, hydraulically operated, or similar. The linkage assembly 26 may include a pivot bar 30 having first and second opposite ends 32, 34 respectively. The pivot bar first end 32 is pivotally connected to the slide plate 20 and the pivot bar second end 34 is operatively connected to the hemming roller 22. For example, the hemming roller 22 may be rotatably mounted on a mount 36 via an axle 38, and the mount 36 may be connected to the pivot bar 30. A stop 39 may be mounted to the slide plate 20. The stop 39 limits the pivotal movement of the pivot bar 30. The linkage assembly 26 further includes a link bar 40 having first and second opposite ends 42, 44 respectively. The link bar first end 42 is pivotally attached to the pivot bar second end 34 adjacent the hemming roller 22. The linkage assembly 26 also includes a bell crank arm 46 having first and second opposite ends 48, 50 respectively. The bell crank arm first end 48 is pivotally connected to the link bar second end 44. The bell crank arm second end 50 is pivotally connected to the pivot actuator 24. For example, the bell crank arm second end 50 may be pivotally connected to an end of a piston 52 of the pivot actuator 24. The bell crank arm 46 is also pivotally connected to the slide plate 20 intermediate the bell crank arm first and second ends 48, 50. It should be understood, however, that the linkage assembly 26 may have a different mechanical structure for pivoting the hemming roller 22. The hemming roller 22 may be pivoted by other mechanical or electromechanical arrangements. For example, the apparatus 10 may include a servo positioner for adjusting the hemming roller 22 between various pre-hemming and final hemming angular positions.

The pivot actuator 28 may be mounted on the slide plate 20 by a fastener 54 or similar. Therefore, the linkage assembly 26 and pivot actuator 28 remain stationary relative to the slide plate 20 as the slide plate 20 moves relative to the mounting member 12. The slide actuator 24 may be mounted on the mounting member bracket 16. Hence, the slide actuator 24 is fixed relative to the mounting member 12.

The mounting member bracket 16 may include a linear track 56. The slide plate 20 is operatively engaged with the linear track 56 and slidable along the linear track. The linear track 56 may include a pair of rails 58, and the slide plate 20 may include a pair of bearing blocks 60 engaged with the pair of rails 58.

Turning to FIG. 3, in an alternative embodiment, a robotic roller hemming apparatus 110 includes a mounting member 112 and operatively connected tracking roller 118 and hemming roller 122. The hemming roller may include an indexing portion 180 that is cooperable with an edge of an anvil 168 that allows for indexing of the hemming roller 122 between pre-hemming and final hemming positions. In FIG. 3, the hemming roller 122 is shown in the pre-hemming position relative to a workpiece 174 and anvil 168. The final hemming position of the hemming roller 122 is shown in phantom. The roller hemming apparatus 110 may some of the other features described in the first embodiment. For example, the roller hemming apparatus 110 may include a linear rail 156 mounted on the mounting member 112, and a slide plate 120 including bearing blocks 160 that are engaged with the linear rail 156. The hemming roller 122 may be operatively connected to the slide plate 120, and movement of the slide plate 120 adjusts the distance between the hemming roller 122 and tracking roller 118.

With reference to FIGS. 1, 4, and 5, the robotic roller hemming apparatus 10 may be used in a dual-robot roller hemming system 62. The robotic roller hemming system 62 includes a first multi-axis controllable robotic arm 64 having an end effecter 66 that carries a hemming anvil 68. The end effecter 66 may be a robotic tool exchange unit that engages and carries the anvil 68 and allows for easy interchange of the anvil 68 with at least one alternative anvil 70. Interchange of the anvil 68 for an alternative anvil 70 allows the system 62 to hem various workpieces of differing size and shape. The roller hemming system 62 may also include an anvil storage unit 71 for holding the at least one alternative hemming anvil 70. Each anvil 68, 70 may include a nesting feature (not shown) that cooperates with features in the anvil storage unit 71 to hold the anvils 68, 70 in the storage unit. The anvil 68 may also include an attachment device 72 for temporary attachment of the anvil to a workpiece 74. The attachment device 72 may include an arrangement of vacuum cups. The vacuum cups may be operated by a vacuum suction source that can be activated to hold the anvil 68 to the workpiece 74 and deactivated to release the anvil from the workpiece. The first robotic arm 64 may include a location unit 76 for positioning the anvil 68 relative to the workpiece 74. The location unit 76 may include a vision system and/or a simple measuring system.

The robotic roller hemming system 62 also includes a second multi-axis controllable robotic arm 78 has a roller hemming head, such as the roller hemming apparatus 10, at an end thereof. The second robotic arm 78 can manipulate the hemming apparatus 10 to position the hemming roller 22 about an edge of the workpiece 74 on one side of the workpiece, and the anvil 68 may be positionable adjacent the workpiece about a side opposite the hemming roller 22.

The tracking roller 18 is engagable with the anvil 68 to aide in guiding the roller hemming apparatus 10 along the anvil. The slide plate 20 is linearly moveable to adjust the distance between the hemming roller 22 and tracking roller 18, thereby allowing for compression of the workpiece 74 and the anvil 68 between the hemming roller 22 and the tracking roller 18.

With reference now to FIGS. 1, 4, and 6, the anvil 68 may include a tracking surface 82 and a hemming surface 84. The first robotic arm 64 may be employed to position the anvil hemming surface 84 adjacent the workpiece 74, such as along an edge of the workpiece to be hemmed. After the first robotic arm 64 positions the anvil hemming surface 84 adjacent the workpiece 74, the anvil 68 may be temporarily attached to the workpiece to stabilize the anvil relative to the workpiece. For example, if the anvil 68 includes vacuum cups 72, a suction device may be activated so that the vacuum cups 72 hold the anvil 68 against the workpiece 74.

The pivot actuator 28 may be activated to adjust the hemming roller 22 into the pre-hemming position. In the pre-hemming position, the hemming roller 22 may be at a 45° angle relative to the edge of the workpiece 74. Alternatively, the hemming roller 22 may pre-hem the workpiece at 30° and 60° angles relative to the workpiece edge. The second robotic arm 78 is employed to position the roller hemming head, such as roller hemming apparatus 10, relative to the workpiece 74 and to the anvil 68 such that the tracking roller 18 contacts the anvil tracking surface 82 and the hemming roller 22 engages the workpiece 74. For example, the slide plate 20 may be actuated to engage the tracking roller 18 with the anvil tracking surface 82 and to engage the hemming roller 22 with the workpiece 74 prior to pre-hemming. The pressure the hemming roller 22 exerts on the workpiece 74 can be adjusted by varying the amount of force exerted on the slide plate 20 by the slide actuator 24.

When the tracking roller 18 and hemming roller 22 are properly engaged, the second robotic arm 78 is employed to move the roller hemming apparatus 10 along the anvil 68 such that the tracking roller 18 follows the anvil tracking surface 82 and the hemming roller 22 pre-hems the workpiece 74. Next, the hemming roller 22 may be adjusted to the final hemming position. In the final hemming position, the hemming roller 22 is at a 90° angle relative to the edge of the workpiece 74. The second robotic arm 78 is then employed to move the roller hemming apparatus 10 along the anvil 68 such that the tracking roller 18 follows the anvil tracking surface 82 and the hemming roller 22 final hems the workpiece 74.

A path followed by the hemming roller 22 during the pre-hemming stroke may also be followed by the hemming roller during final hemming. In other words, the pre-hemming and final hemming paths may be essentially identical. Likewise, the tracking roller 18 may follow the same path along the anvil track surface 82 during pre-hemming and final hemming. Moreover, during final hemming, the hemming roller 22 may follow the hemming path in the same direction of travel as during pre-hemming. In this case, the second robotic arm 78 may move the hemming roller 22 forward during pre-hemming, return the hemming roller 22 to its starting position by generally moving the hemming roller 22 in a reverse direction, and then move the hemming roller 22 forward during final hemming. Further, while moving the hemming roller 22 back to its starting position after pre-hemming, the hemming apparatus 10 may adjust the hemming roller 22 from its pre-hemming angular configuration to its final hemming configuration.

Alternatively, for final hemming, the hemming roller 22 may follow the hemming path in a reverse direction relative to a direction of travel followed during pre-hemming. In this case, the second robotic arm 78 moves the hemming roller 22 forward during pre-hemming from a first location to a second location, and then moves the hemming roller 22 in reverse during final hemming from the second location back to the first location.

After the hemming roller 22 final hems the workpiece 74, the slide plate 20 may be actuated to disengage the tracking roller 18 with the anvil tracking surface 82 and the hemming roller 22 with the workpiece 74 after final hemming. More specifically, the slide actuator 24 moves the slide plate 20 outwardly relative to the mounting member 12 to increase the distance between the tracking roller 18 and hemming roller 22. Finally, the second robotic arm 78 may be employed to move the roller hemming apparatus 10 away from the workpiece 74, and the first robotic arm 64 may be employed to move the anvil 68 away from the workpiece. If the anvil 68 has been temporarily attached to the workpiece 74 by attachment device 72, the attachment devices 72 are deactivated/released prior to the first robotic arm 64 moving the anvil 68.

Although the invention has been described by reference to specific embodiments, it should be understood that numerous changes may be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims. 

1. A robotic roller hemming apparatus comprising: a mounting member including face for operative connection of the mounting member to a multi-axis controllable robotic arm, and a bracket extending from said face; a tracking roller mounted on said bracket; a slide plate operatively connected to said bracket and slidable relative to said bracket; a hemming roller operatively connected to said slide plate proximate said tracking roller for roller hemming nested metal panels therebetween said hemming and tracking rollers; and a slide actuator connecting said bracket and said slide plate for moving said hemming roller toward and away from said tracking roller.
 2. The robotic roller hemming apparatus of claim 1, including a linkage assembly operatively connected to said mounting member and said hemming roller for pivoting said hemming roller relative to said mounting member; and a pivot actuator for actuating said linkage assembly to pivot said hemming roller.
 3. The robotic roller hemming apparatus of claim 2, wherein said linkage assembly includes: a pivot bar having first and second opposite ends, said pivot bar first end being pivotally connected to said slide plate and said pivot bar second end being operatively connected to said hemming roller; a link bar having first and second opposite ends, said link bar first end being pivotally attached to said pivot bar second end adjacent said hemming roller; and a bell crank arm having first and second opposite ends, said bell crank arm first end being pivotally connected to said link bar second end and said bell crank arm second end being pivotally connected to said pivot actuator; said bell crank arm being pivotally connected to said slide plate intermediate said bell crank arm first and second ends.
 4. The robotic roller hemming apparatus of claim 3, including a stop mounted to said slide plate, said stop limiting the pivotal movement of said pivot bar.
 5. The robotic roller hemming apparatus of claim 2, wherein said pivot actuator is mounted on said slide plate.
 6. The robotic roller hemming apparatus of claim 1, wherein said slide actuator is mounted on said mounting member bracket.
 7. The robotic roller hemming apparatus of claim 1, wherein said mounting member bracket includes a linear track, and said slide plate is operatively engaged with said linear track and slidable along said linear track.
 8. The robotic roller hemming apparatus of claim 7, wherein said linear track includes a pair of rails, and said slide plate includes a pair of bearing blocks engaged with said pair of rails.
 9. A robotic roller hemming system comprising: a first multi-axis controllable robotic arm having an end effecter that carries a hemming anvil; a second multi-axis controllable robotic arm having a roller hemming head at an end thereof, said roller hemming head including a tracking roller and a multi-positional hemming roller capable of performing both pre-hemming and final hemming operations; said hemming roller being adjustable between pre-hemming and final hemming positions and cooperable with said tracking roller and anvil to pre-hem and final hem a workpiece; wherein said hemming roller performs pre-hemming and subsequent final hemming of said workpiece sequentially along a single hemming path.
 10. The robotic roller hemming system of claim 9, wherein said hemming roller is positionable about an edge of said workpiece on one side of the workpiece; and said anvil is positionable adjacent the workpiece about a side opposite said hemming roller.
 11. The robotic roller hemming system of claim 9, wherein said first robotic arm end effecter comprises a robotic tool exchange unit for interchanging said anvil with at least one alternative anvil.
 12. The robotic roller hemming system of claim 11, including an anvil storage unit for holding said at least one alternative hemming anvil.
 13. The robotic roller hemming system of claim 9, wherein said anvil includes an attachment device for temporary attachment of said anvil to said workpiece.
 14. The robotic roller hemming system of claim 13, wherein said attachment device includes an arrangement of vacuum cups.
 15. The robotic roller hemming system of claim 9, wherein said first robotic arm includes a location unit for positioning said anvil relative to a workpiece.
 16. The robotic roller hemming system of claim 9, wherein said hemming roller includes an indexing feature cooperable with an edge of said anvil that allows for indexing of said hemming roller between pre-hemming and final hemming positions.
 17. The robotic roller hemming system of claim 9, wherein said roller hemming head includes a servo positioner for adjusting the hemming roller between various pre-hemming and final hemming angular positions relative to said anvil.
 18. The robotic roller hemming system of claim 9, wherein said roller hemming head includes an actuator for adjusting the hemming roller between various pre-hemming and final hemming angular positions relative to said anvil.
 19. The robotic roller hemming system of claim 9, wherein said tracking roller is engagable with said anvil to aide in guiding said roller hemming head along said anvil.
 20. The robotic roller hemming system of claim 9, wherein said roller hemming head includes a slide unit for compressing said workpiece and said anvil between said hemming roller and said tracking roller.
 21. The robotic roller hemming system of claim 20, wherein said slide unit linearly moves said hemming roller to adjust the distance between said hemming roller and said tracking roller.
 22. A method for robotic roller hemming comprising the steps of: providing a first multi-axis controllable robotic arm having an end effecter that carries a hemming anvil having a hemming surface and a tracking surface; providing a second multi-axis controllable robotic arm having a roller hemming head at an end thereof, said roller hemming head including a hemming roller adjustable between pre-hemming and final hemming positions and a tracking roller proximate said hemming roller; employing said first robotic arm to position said anvil hemming surface adjacent a workpiece; adjusting said hemming roller to said pre-hemming position; employing said second robotic arm to position said roller hemming head relative to said workpiece and said anvil such that said tracking roller contacts said anvil tracking surface and said hemming roller engages said workpiece; employing said second robotic arm to move said roller hemming head along said anvil such that said tracking roller follows said anvil tracking surface and said hemming roller pre-hems said workpiece; adjusting said hemming roller to said final hemming position; and employing said second robotic arm to move said roller hemming head along said anvil such that said tracking roller follows said anvil tracking surface and said hemming roller final hems said workpiece.
 23. The method of claim 22, wherein a path followed by said hemming roller during pre-hemming is also followed by said hemming roller during final hemming.
 24. The method of claim 23, wherein during final hemming, said hemming roller follows said path in the same direction of travel as during pre-hemming.
 25. The method of claim 23, wherein during final hemming, said hemming roller follows said path in a reverse direction relative to a direction of travel followed during pre-hemming.
 26. The method of claim 22, further including the step of: after said first robotic arm positions said anvil hemming surface adjacent said workpiece, temporarily attaching said anvil to said workpiece to stabilize said anvil relative to said workpiece.
 27. The method of claim 22, wherein said roller hemming head includes a slide unit for engaging and disengaging said tracking roller with said anvil tracking surface and said hemming roller with said workpiece; the method further including the steps of actuating said slide unit to engage said tracking roller with said anvil tracking surface and said hemming roller with said workpiece prior to pre-hemming; and actuating said slide unit to disengage said tracking roller with said anvil tracking surface and said hemming roller with said workpiece after final hemming.
 28. The method of claim 22, further comprising the steps of: after said hemming roller final hems said workpiece, employing said second robotic arm to move said roller hemming head away from said workpiece; and employing said first robotic arm to move said anvil away from said workpiece. 